1. Technical Field of the Invention
The present invention relates to formation testing, particularly related to drilling wells in hydrocarbon-containing reservoirs for exploration, delineation, production and injection. More specifically, the present invention relates to a device for formation testing when drilling, a method for determination of the fracturing pressure in a lower isolated open part of a well-bore, a method for determination of pore pressure in a lower isolated open part of a well-bore, a method for determination of formation properties in a lower isolated open part of a well-bore and a device for formation testing of a production well.
2. Description of the Related Art
When developing a hydrocarbon-containing field, a number of tasks should be solved as good as possible. Delineating the deposit and placing surface installations and wells, are some of the tasks to solve. Determining the well design, drilling program, production program and further development of the field after a while, are essential tasks.
While drilling, the pressure in the open part of a well can, in general, be held between the pore pressure and the fracturing pressure. When developing long wells, wells of low flow cross section and wells in depleted formations, it can be very challenging to find a functional solution for the casing program, drilling program and further development of the field. This is mainly because the available operational window is very narrow and additionally the knowledge about rock mechanics of the well-bore and possible formations for penetration often are insufficient. For the above-mentioned objectives determining the stress condition of the underground is essential. The stress condition and pressure change as the reservoir is produced. Maintaining pressure and stress condition can be achieved by injecting water and/or gas into the reservoir. A rock mechanical model including data from the whole development and service life of the field, and with frequent updates, is essential to achieve optimal development and production. Data of high quality is crucial for establishing and developing the model. Pore pressure, stress condition, fracturing pressure, temperature, geological weaknesses, information from underground samples, seismic and electromagnetic data are some of the parameters and measurements that are used for developing and updating the rock mechanical model.
A plurality of equipment and methods exist for measuring stress, pore pressure and flow potential in and through underground formations. Pressure build-up in an isolated section of an open part of a well-bore is often used for determining fracturing pressure. Reduction of pressure in an isolated section in an open part of a well-bore is often used to determine pore pressure and stresses in the formation. Likewise the formation properties in an isolated section of an open part of a well-bore can be determined by pumping in fluid and measuring pressure and back-flow over time from the formation. Further, equipment inter alia based on measuring resistivity and propagation and reflexes of acoustic waves, for the determination of occurrence and orientation of cracks, also exists.
In U.S. Pat. No. 6,148,912 formation evaluation is described during drilling, whereby pressure measurements are undertaken in a zone isolated by the use of packers on the drill string. In U.S. Pat. No. 4,453,595, a method is described for determining the fracturing pressure in an isolated lower part of a well-bore, whereby a controlled pressure increase exceeding a nominal pressure is generated with a separate cylinder/piston device providing controlled volume variation of the isolated lower well-bore chamber.
A demand exists for a device and methods simplifying the determination of formation properties in the underground in relation to drilling, particularly at and in front of a drilling bit, and particularly so that said properties can be determined without first drilling through the formation. There is a particular demand for determining fracturing pressure in a lower open part of a well-bore without significant risk of damaging the formation permanently by fracturing uncontrolled in a way lowering the fracturing pressure for subsequent drilling. There is a particular demand for a device and methods that are simple to use and that are flexible with respect to determining the fracturing pressure, closure pressure of the cracks (least horizontal stress), pore pressure and further formation properties quickly and effectively, without significant risk for damaging the underground formation and without significant risk for health, environment and security. There is a demand for a device that easily can be adapted to measure over smaller or larger isolated test zones. There is a particular demand for a device and methods for determining the formation properties, which also makes it simple to establish the integrity of the formation before subsequent drilling. Further, there is a demand for a device for formation testing in a production well.